If it's just a few (like 20 or less) you may simply want to make a calculation field, result is text, defined like:

Case(

Field = "Y" ; "Yes" ;

Field = "N" ; "No" ;

Field = "G" ; "Gallons" ;

Field = "F" ; "False" )

If there are many field occurrences on the layout, or many many abbreviations, you may want to create a translator table with one record for each abbreviation.

Link it to the parent by the abbreviation, but put the translator table's field on your layout. The abbreviation will link to the correct record on your translator table and pull the correct full work over.

I have to be messing up somewhere. Please see attached pics. Am I doing this right? Also the use of a translator table sounds interesting. Could you explain in possible more noobishly how to set that up.